The objective of this project is a better understanding of the structure of RNA tumor viruses and of the events in infected cells involved in virus replication and cell transformation. Rauscher leukemia virus particles will be dissociated with detergents, solvents, or enzymes and fractionated into subviral components, and their ultrastructure and polypeptide composition will be determined. Cross- linking reagents and immunoferritin procedures will also be used; the aim of these studies is to determine the arrangement of the major structural polypeptides of the virion as well as to obtain each of these polypeptides in pure form. To localize viral macromolecules in infected cells, antisera to purified antigens will be prepared and conjugated with electron-dense markers. Intracellular tagging will be achieved by use of serum albumin embedding, partial disruption of the cell membrane, and examination of isolated organelles. The effects of protease inhibitors and inhibitors of glycosylation on the distribution of intracellular antigens will be determined. Cells infected with temperature-sensitive mutants of Rous sarcoma virus will be studied by electron microscopy. Intracytoplasmic and extracellular virus particles from mouse L1210 leukemia cells, which are present in large amounts and may be representative of intracytoplasmic A and extracellular B-type particles, will be isolated and their structural and biological properties determined.